A frequently used type of electronic force-measuring device includes a mechanical/electrical measurement transducer which converts the force acting on the force-measuring device into a corresponding electrical measurement signal. Analogously, the measurement conversion in a balance generates an electrical measurement signal which corresponds to the weight force exerted by the weighing object. Following the conversion, the measurement signal is transmitted to a display or to a further processing device, for example a master computer or a system controller.
Before the electrical measurement signal is displayed or processed further, it is in most cases sent to a signal-processing stage which is arranged as a pre-processing unit in the signal path ahead of the display and/or the further processing section. In this pre-processing stage, the measurement signal is processed, evaluated and in some cases corrected and amplified.
To make the measurement signal compatible with the display or a further processing stage, it is normally converted into a suitable format. For example in the case of an analog indicator, the voltage values of the measurement signal are adapted to the range that can be represented on the display or, in the case of a digital indicator, corresponding digital output values are assigned to the measurement signal.
The conversion can generally be described by a display function which assigns corresponding output values to the input values. The values of the measurement signal represent the input values of the display function, and the output values of the display function are presented on the display or passed along for further processing. The conversion of the measurement signal into digital output values can be described for example by a display function with a step-shaped characteristic, to that discrete output values are assigned to the continuous input values.
Force-measuring devices, specifically balances, are typically used to weigh individual objects, and also in automated production- and test systems for the weighing of larger quantities of goods. A force-measuring device of this kind has to meet the requirements of a high measuring accuracy and high reproducibility of the measurements and thus a high degree of stability. The force-measuring device should further be of a simple and cost-effective design.
Particularly in applications where the measurement accuracy is high, it is known that even the smallest disturbances of the measurement signal can lead to considerable instabilities of the output values. These instabilities cause frequent, rapid changes of the values presented in the display, i.e. so-called display fluctuations. As a result of the display fluctuations, it becomes difficult or even impossible to read these values, in particular their lowest decimal places or finest scale graduations. As a further consequence, these instabilities can cause problems such as inaccuracies downstream in the processing.
The existing state of the art offers a variety of methods to solve these problems. For example in U.S. Pat. No. 3,826,319, a balance with a digital display is disclosed where after a change of the weighing load the lowest decimals are suppressed and are subsequently restored one by one in the display. However, suppressing the display digits causes a loss of accuracy, so that this method is not suitable when a high accuracy is required.
Losses of accuracy can be avoided to a certain extent through processing methods in which a stabilization of the display is achieved by averaging the measurement signal. However, the averaging process will cause a deterioration of the response of the force-measuring device to load changes, i.e. the ability of the display to follow the input signal is slowed down and the time required for a measurement is increased.
The existing state of the art offers a variety of methods to shorten the response time regardless of the averaging. For example DE 102005021547 discloses the concept of temporarily interrupting the averaging process during a change of the weighing load in order to be able to follow the load changes more rapidly. However, this method requires a relatively elaborate circuit design.
An unmet objective of the prior art is to provide a method of processing the signal of a force-measuring device, specifically a balance, and to further provide a force-measuring device that is suitable to carry out the method and satisfies exacting requirements in regard to measurement accuracy, stability and response time as well as in regard to simplicity and cost-effectiveness in its design and operation.